In general, polybutene is obtained by polymerizing an olefin component having 4 carbon atoms (C4) derived during a naphtha cracking process using a Friedel-Crafts catalyst, and has a number average molecular weight (Mn) of approximately 300 to 5,000. A residuum remaining after 1,3-butadiene is extracted from C4 raw materials is referred to as C4 raffinate-1, which includes paraffins such as isobutane, and normal butane, and olefins such as 1-butene, 2-butene, isobutene, etc. Among these components, the content of isobutene is in a range of approximately 30 to 50% by weight. The C4 raffinate-1 is generally used to prepare an octane booster such as methyl-t-butyl ether (MTBE) or polybutene. In this case, since isobutene has the highest reactivity among the olefin components of the C4 raffinate-1, the resulting polybutene is mainly composed of isobutene units. In addition, polybutene is often prepared from a butane-butene (B-B) fraction or high-purity isobutene, which is a C4 mixture derived during a petroleum refining process.
Viscosity of polybutene increases with increase in molecular weight. For example, polybutene has a viscosity of approximately 4 to 40,000 centistokes (cSt) at 100° C. In addition, polybutene is thermally cracked at a temperature of 300° C. or higher without leaving remnants behind, and is highly soluble in a lubricant or a fuel since the polybutene has a branched alkyl structure. Therefore, the polybutene is often used as an anti-scuff agent or a viscosity index improver when added to car engine oil, and also used as a detergent when mixed with a fuel in internal combustion engines for automobiles.
In the prior art, since polybutene was generally used in pressure-sensitive adhesives, adhesives, and insulating oils, products having high reactivity have not been preferred. In recent years, however, demand for polybutene, which is highly reactive since polar groups are incorporated to polybutene, has steadily increased with increasing use as fuel detergents or lubricant additives. Therefore, a highly reactive polybutene to which polar groups may be incorporated due to reactivity has been widely used for fuel detergents or lubricant additives. A polyisobutenyl succinic anhydride (PIBSA) prepared by reaction of a maleic anhydride with a double bond at the end of a highly reactive polybutene by means of heating has been widely used in products which may be obtained by incorporating polar groups thereto. In this case, PIBSA is used as an intermediate when most lubricant additives or fuel detergents are prepared. For example, when double bonds in polybutene used to prepare PIBSA are positioned at the end of polybutene, PIBSA is obtained with high yield. On the other hand, when double bonds are positioned inside polybutene, and especially when double bonds are increasingly substituted with alkyl groups, the yield of PIBSA decreases due to low reactivity caused by steric hindrance.
Forming a double bond at an end of a molecule and terminating polymerization of a polymer means production of compounds which do not follow a general theory of chemical kinetics. The use of a complex catalyst in which a catalyst and a cocatalyst are mixed is most effective in preparing highly reactive polybutene which is difficult to produce in this way. However, such a complex catalyst has difficulties in operation of plants, for example, installing a tank for preparing a complex catalyst and producing various products having different molecular weights, but there are no patents proposing solutions and countermeasures to the difficulties.
Prior to use of highly reactive polybutene, PIBSA was prepared from typical polybutene, that is, non-reactive polybutene. One method of enhancing reactivity of non-reactive polybutene includes chlorinating polybutene with chlorine gas (a chlorination reaction), and then reacting the chlorinated polybutene with a maleic anhydride to prepare PIBSA, thereby finishing final products. In this case, however, high costs are required to prevent corrosion of a reactor, and a large amount of a basic solution should also be used to neutralize unreacted chlorine gases, which are undesirable in economic and environmental aspects. Further, when PIBSA having an increased content of chlorine is used as a fuel additive and the like, internal combustion engines such as car engines may suffer corrosion, and chlorine may be discharged as an exhaust gas. Therefore, such problems have been addressed thorough a method of preparing a lubricant additive and a fuel detergent using a highly reactive polybutene.
Highly reactive polybutene has an advantage as it has a higher content of vinylidene. The reason will be explained below based on techniques generally known in the art. Highly reactive polybutene is subjected to an Ene reaction (also known as an Alder-ene reaction) to react with maleic anhydride at approximately 230° C. PIBSA prepared by such a reaction is allowed to react with an alkylamine to prepare polyisobutenyl succinic imide (PIBSI), and a diluent having a high boiling point is mixed with the PIBSI to prepare a fuel detergent and a lubricant additive. The yield of PIBSA varies according to the content of vinylidene in the highly reactive polybutene. As the content of vinylidene increases, the PIBSA has superior qualities, and the yield of PIBSA also increases. Here, the higher yield of PIBSA means the higher yield of PIBSI, indicating that an active ingredient serving as a detergent is present in a high content. Therefore, it is revealed that it is important to prepare a highly reactive polybutene having a high content of vinylidene.
Evolution of non-reactive polybutene used in such a lubricant additive or fuel detergent into highly reactive polybutene is a process which has a process improvement in which one reaction step is reduced and is environmentally friendly since it is possible to remove toxic chlorine (Cl2) gas. Therefore, research on preparation of highly reactive polybutene, which has a vinylidene content of at least 70%, more preferably at least 85% but does not include chlorine causing corrosion of devices, has been conducted to enhance reactivity of polybutene. Boron trifluoride (BF3), which is used to yield a highly reactive polybutene having a relatively higher content of vinylidene than other Lewis acids, is generally used as a Friedel-Crafts catalyst to prepare the highly reactive polybutene. U.S. Pat. Nos. 4,605,808, 5,068,490, 5,191,044, 5,408,018, 5,962,604, and 6,300,444 disclose a method of preparing highly reactive polybutene, wherein the highly reactive polybutene has a vinylidene content of at least 70%, more preferably at least 80% when boron trifluoride or a complex thereof is used together with a cocatalyst such as water, ether, alcohol, etc.
Referring to the patent documents, the molecular weights of polymer products are very closely related with the catalytic activity. That is, when a complex catalyst having a high catalytic activity and a low cocatalyst/main catalyst molar ratio is used, products having high molecular weights are produced. On the other hand, when the molar ratio of the complex catalyst gradually increases, catalytic activity may be lowered, leading to production of products having low molecular weights. In addition, the content of vinylidene indirectly implies that a cocatalyst such as alcohol and ether, and a complex catalyst with degraded catalytic activity are used to enhance reaction selectivity of isobutene, thereby preparing a highly reactive polybutene having a high content of vinylidene.
Registered U.S. Pat. No. 5,068,490 discloses a method of preparing polybutene having a vinylidene content of at least 80% using a complex of boron trifluoride and ether containing at least one tertiary alkyl group as a catalyst. Such a method has an advantage in that a low level of isomerization reaction occurs even when long contact times are maintained. Meanwhile, referring to the embodiments of Registered U.S. Pat. No. 5,068,490, the best results are realized when isopropyl t-butyl ether having both a secondary alkyl group and a tertiary alkyl group is used, but isopropyl t-butyl ether has a drawback in that it is very expensive, and isopropyl t-butyl ether must be personally manufactured as commercial sources are unavailable. Registered U.S. Pat. Nos. 5,408,018 and 5,962,604 disclose a method of preparing polybutene, which has a vinylidene content of at least 80% and a narrow molecular weight distribution as well, using a complex of secondary alcohol and boron trifluoride as a catalyst. However, the method has many limitations on reaction conditions in which the contact is maintained at a temperature of −10° C. or less for a short period of time, and has a drawback in that a high-purity isobutene raw material should be used to increase the content of vinylidene. Registered U.S. Pat. No. 6,300,444 discloses a method of preparing polybutene using a catalyst (boron trifluoride) and a cocatalyst (ether, alcohol and/or water) in a specified molar ratio. Registered U.S. Pat. No. 6,300,444 is characterized in that a catalyst, a cocatalyst, and a reaction raw material are added together to a reactor to prepare a highly reactive polybutene without forming a complex of the catalyst and the cocatalyst in advance, and a vacuum pump is used to reduce a content of fluorine in the product, but has drawbacks in that it is difficult to obtain a highly reactive polybutene having a high vinylidene content since the catalyst and the cocatalyst cannot be mixed to form a stable complex, and high costs are required since a vacuum pump is used to reduce the content of fluorine in the product.
The highly reactive polybutene is important for vinylidene content (terminal double bond content). Thus, complex catalysts optimized for respective products having different molecular weights are required to prepare highly reactive polybutene having a high vinylidene content. For example, methods of preparing 6 complex catalysts having different molar ratios are required to prepare 6 types of highly reactive polybutenes having different molecular weights. A production plan suitable for market demands should be designed, and thus complex catalysts suitable for use in each of the products having different molecular weights should be prepared to effectively produce the products in consideration of manufacturing costs. That is, complex catalysts should be prepared to match output, and a cycle of preparing a complex catalyst should increase with increase in the number of products having different molecular weights. However, since catalysts should be separately prepared and added to polybutenes having different molecular weights as known in the prior art, manufacturing costs may increase due to increase in labor costs and installations costs for tanks used to prepare the respective catalysts, and the content of vinylidene in the polybutenes is also low. In addition, when only one catalyst is used to prepare polybutenes having different molecular weights, the polybutenes are prepared so that the content of vinylidene in the polybutenes is lower by up to approximately 10%. The content of vinylidene of 10% differs by approximately 6 to 8% due to a difference in reaction yield with a maleic anhydride to prepare PIBSA, and thus corresponds to approximately 10% of PIBSA with a total reaction yield of 70%. As a result, end users will purchase products having a content of vinylidene increased by 10%, indicating that end users will purchase products having a value increased by 10%.
Also, since a main catalyst and a cocatalyst are mixed in exact molar ratios to prepare a complex catalyst, this process may be cumbersome due to many regulations which have to be obeyed during a manufacturing process, for example, injecting the main catalyst and the cocatalyst in fixed amounts, maintaining a proper temperature while a complex is prepared, maintaining a proper injection rate of catalysts to prevent deformation of the catalysts caused by heat occurring during preparation of the complex, etc. Further, when operators hired to run a plant work long hours, an increase in manufacturing costs is also caused, which leads to increase in fixed costs. Therefore, there is an urgent demand for improvement of systems for preparing and feeding a complex catalyst.